Cage assembly for crystals



Aug. 26, 1952 A. w. ZIEGLER CAGE ASSEMBLY FOR CRYSTALS 2 SHEETS-SHEET 1 Filed Jan. 10, 1950 IN VE N TOR A. m Z/EGLER ATTORNEY:

Aug. 26, 1952 A. w. Z|EGLER 2,508,597

CAGE ASSEMBLY FOR CRYSTALS Filed Jan. 10, 1950 '2 SHEETS-SHEET 2 INVENTOR A. WZ/EGLER A T TORNEK Patented Aug. 26, 1952 UNITED STATES PATENT OFFICE CAGE ASSEMBLY FOR CRYSTALS Arthur W. Ziegler, Short Hills, N. J., asslgnor to Bell Telephone Laboratories, Incorporated, New

York, N. Y., a corporation of New York Application January 10, 1950, Serial No. 137,690

g 4 Claims.

This invention relates tothe manufacture of crystals and more particularly to means and methods for assembling and mounting piezoelectric crystal units.

It is common practice in the piezoelectric crystal art to mount crystals. by means of resilient wires cemented or soldered to the crystal surface and in turn supported by structural members, the entire assembly being enclosed within a sealed envelope. The structural members, which may be slender rods or tubes of nickel or an equivalent material, should be susceptible of being formed to close tolerances and have high conductivity so that electrical connection to the crystal may be made therethrough. The rods are held in a spaced array, commonly called a cage, as by end spacers of mica or equivalent material. Metal eyelets or grommets are fixed in the spacers to receive the rods, which may be secured thereto by spot welding or similar means.

Various considerations relating to operating characteristics of the crystals have led to the-use of fine resilient wires which may be of the order of a few thousandths of an inch in thickness, for supporting the crystal on the rods. The mass of the piezoelectric crystal is sufficient so that a severe mechanical shock, such as that experienced if a crystal unit is dropped, may cause separation at the bond between the crystal and the supporting wires, or a permanent displacement of the crystal position. The result may be the introduction of mechanical strains between the crystal and its support which will cause the crystal to vibrate at frequencies otherthan the period for which it was intended.

To avoid such'consequ'ences, it has been the practice to prevent excessive displacement of the crystal by means of bumpers. The bumpers may take the form of mica endpla'tes which are apertured to permit the insertion of a portion of the crystal. The apertures are' 'made s'ufliciently large so that the crystalin'riorm'al vibration will not come in contact with themica spacer, but small enough to prevent'crystal displacement during rough handling 'suflicient to produce the -ill effects described above.

This spacing problem in practice has meant that each different type of crystal has required a set of mica spacers individually designed for its accommodation. This in turn entailed arequir'ement that a large number of small piece parts had to be kept on hand by the factory, which could neither be produced nor handled on amass production basis. vIn addition, the assembly required the use by the factory operator of shims to align the crystal properly With'the mounting 2 cage. This is a laborious and time consuming procedure and frequently results when improp erly done in introducing strains into the supporting wires which would be reflected in operational failures and frequency inaccuracies.

An additional factor is the tendency of the softer synthetic materials, such as ethylen diamine tartrate, commonly known as EDT, to fracture easily on impact. Although the mica and polyethylene fluoride or tefion combination commonly used for the end spacers with synthetic crystals is relatively soft, it has been found that particles from the crystal surface may be broken off by repeated contacts with the teflon after displacement of the crystal from its normal position. This result has even obtained with the harder piezoelectric materials such as quartz, in spite of the comparative softness of all the mica bumper material there used.

The present invention eliminates the difficulties referred to above by providing a metal-tometal bumper contact in a form which permits free floating mounting during the assembly of the crystal unit. In a crystal unit constructed in accordance with the invention, bumper rods are secured to each end of the crystal. The mica spacers forming the cage ends are provided with bumper tubes of internal diameter substantially greater than that of the external diameter of the bumper rods. Thus, if displacement of the crystal occurs, it will be limited by the contact of the metal bumper rod with the metal bumper tube. The rods are '50 located on the crystal that they do not interfere with its electrical characteristics, once the initial adjustment for frequency has been made during manufacture. The size of the rods is kept to a minimum consistent with ability to restrain the crystal during displacements. Hence, they exert a minimum effect on the crystal vibratory characteristics.

The invention comprehends in addition to the particular bumper system, a method of caging the crystal which is adapted to prevent the setting up of strains in the supporting assembly and to aid in the accurate alignment of the crystal within its cage.

It will thus be seen that a primary object of the invention is to provide an improved crystal supporting system, and means and a method for the free floating mounting of the crystal within the improved system.

Another object is the elimination of frequency variations resulting from the dislodging of minute particles of the crystal by contact with the bumper.

An additional object is the elimination of the necessity for laborious shimming operations in aligning the crystal within its cage.

A still further object is theprovisicn of a.meth-- od and tools for accomplishing airapid assemhly,

of free floating accurately aligned crystalxunitse;

These and other objects may be achieved by the use of the embodiments illustrated; but=it=-is-tobe understood that the embodiments asshown'are Fig. l is alperspective View of a crystal unit embodying. the. bumper system ofv the. invention, portions of. theunit beingbroken away to illustrate some. of the. details with greater clarity ;v

Fig. 2 is a perspective-view to an enlarged scale showing. detailsof constructionofatool for use intheassembling process Fig.8 is a fragmentary view showing .d'etail'slof the bumper system; I

Fig. 4 is a view-,partially in section,.illustrating the. first stagein. a. prefenedl method .Iof. .caging a-crystal;

Fig. ..5-is a.view partially. insection showinganother stage in the .caging operation..ap.plicable to the methodof whichltheifirststage.is, illustrated in Fig. land to another preferred method ofcaging; and

Fig. 6 shows the final .stageoi. .the..comp1eted cagin operation arrived at by either or themeferred methods of. caging. described.

The inventiomas it is incorporatedina .unit designed for. use. withelongated .rectangular piezoelectric. crystals-supported by resilient wires secured. tothe crystals .near..their longitudinal mid-.pointsis sho.wn;in-Fig. 1.... A sealed crystal unit,.generally designated as 1, includes in .addi-.- tionto. a cage-structure, a base. 2 andaglass. or metal envelope. .4 securedthereto. Connecting terminals .5 extend through: the. base 2 of. theenvelope. 4, and are joined toconnecting leads. 6 which are sealed throughth'e press! of the en.- velope. Within the envelope,.connecting. leads 6 are bent to form supportsfor the .straights, or upright connecting and supporting cage. rods .9, which are" made of any readilyformed, substantially rigid supporting material" having good electrical conductivity, such as'nickel. To the rods 9 are fixed by means such-as soldering at 1B or other conventional arrangements, resilient supporting wires H. Supporting wires H, which may be of the order of afew mils in diameter, may be provided with quarter wave solder balls iii, to prevent the transmission through support wires H to the-cage support rods 9 of energy from the crystal 54. Crystal i4 is secured to the support wires H by conventional means,-such as soldering to silver paste spotsor .by special adhesive attachments. The'-connection may also bemade by the use of theheaded wire technique when it. is desired to secure. greatercontact area with the crystal.

The crystal I4 has been shown as having substantial mass, and a single electrode coating area on each major face. Hence, four cage support rods 8 have been provided, with two support wires H joined to each side of the crystal. Many of the crystals used with mountings of this type have split-or-dlvided coatings, that is, there is a separatioirbetween portions'zonthe coating covering a major face of the crystal, with separate connections between each of the coating portions and the remainder of the electrical circuit. Crystals embodying such divided platings are shown in Figshxl to.-=6;;.-inclusiye, where the central longitudinal} typ'e',rofi--..division is illustrated. Other types .oisplit coating arrangements may require difierent arrangements of the supporting wires, butit -is to-be understood that such variations are-contemplated by the present invention.

' The cage rods 9 are maintained in a fixed positionhyvirtue. of beingfixed throughupper and lower imic'a end. spacers. .Iti and l ,1, respectively. Aiconyenientv methodlfo'ri thussecuring the rods and mica spacers in the cage assembly, generally denominated .as 19, involvesithe. use of grommets or eyeletslll Iwhi'clr' may beset fixedly into. the mica .spacersJtiand fflif Rods. 9. 'may. be secured to.-grommets. 2.6? by. spot-.welds..2 I, soldering or equivalent .ineansa Centrally of.l'".the ..upper.andlower mica end spacers I 6. andfllijthere isidisposed a. bushing 22, ingwhich are-fixedmpper: andlower bumper tubes Errand.24,"resp.ectively, Bumper rods 25 are secured' tQtherenter ofleach'endof, the crystal i l by. any. means which; will. not. interfere with the vibrationahcharacteristicsrofthe. crystal. When usedwith-synthetic. crystals such as EDT for example,. the. humpenrods. 25. may be fixed in the end. of.-.the.crystal,.on cemented to. the crystal by conventional techniques.

In. case the .crystalds.v relatively thin,.the area of attachment. might overlapa .small portion of the. sides of .the-. .crystal for-greater, mechanical strength,:being careful tQ-remoVe enough of the electrode. coating...toavoid. short-circuiting the separate. electrodeiareasr. The bumper rods 25 are of, a-diametersubstantially lessthan the inner .diameterqof thebumper tubes '23 and 2 1, so that irr ordinary operation'there will be no con.- tact. :bet-weenthe bumper. rods andtthe bumper tubes. A

The.inside..diameter..oi the-.bump ertubes 23 and Zkshould not be-so'great however; that in floating the. crystalhthe-points. of attachment 3'! of the rods to. the-crystal might. enter the bumper :tubes andepermit. contact. between the tube. and..theezcrystal platee The bumper rod 25 will,.. in..a; properly adjusted crystal unit, be centeredein-,.;but=-spacedrrom. the bumper tube asbest seen-.in theenlargedyiew of. Fig. 3. Rods 25. shouldabejust long enough. so that they will not disengage'iromvthedoumper:tubes,'23 and 24 when maximumraxiah movement occurs.

The metho.d:-of:rfioating: on aligning the crystal properly in the; cage-:to produce. the; finished cage assembly l9 as seen in Fig. 6 involves the useof auxiliary tools;v Onemf such. .tools is: shown in Fig. 2 and itSillSfij-Wi'l]; be discussedin. connection with the:methodsofrcaging;the crystal, which are apart ot-the;presentyinvention.

Previous :methodsrof caging have required individuaL-treatment for-.eachisize' and type of bumperized-.xzunit,;,because. of the many variations inwidt-h;rthicknessi'and length of the crystals involved; The-improvedmethod here idescrihed permitsicagingra: wideirange of crystal sizes in a single size of cage, and making the entire adjustment in the spacing of the bumper tubes.

The first step is the production of the cage structure indicated generally as [9. Rods'e are inserted into the eyelets or grommets 20 fixed in mica end spaces l6 and IT, as shown inthe upper portion of Fig. 4. Fig. 4 shows the general relation of the parts prior to final assembly and it is to be understood that in the actual assembly of the cage 19, the crystal I4 is not present in the initial step. Grommets 20 are then spot welded or crimped securely to the rods 9 to form the cage assembly I9, in substantially the position shown in Fig. 5.

The next step in the production of the cage structure is the insertion of bumper tubes 23 and 24 in bushings 22 of both upper and lower mica spacers l6 and l!, the general practice being thereafter to solder one of the bumper tubes, usually the lower one to the bushing. Following this, the two floating tools 26 are inserted in these bumper tubes. These tools each consist of a shaft 21 on which is mounted a head 29. The position of the head 29 axially of shaft 21 is adjustable under the control of set screw 30. The shaft 21 is of such a diameter as to fit smoothly within one of the bumper tubes. After the insertion of these tools, a resilient locking pin 35 is arranged to snap into the transverse locking groove 34 at the end of shaft 21. The head 29 is then adjusted so that no play exists between the tools and their respective bumper tubes. It is seen that the locking pin prevents the bumper tubes 23 and 24 from falling out of bushings 22 during further handling of the cage.

A crystal I4 is then placed in the cage so that the bumper rods 25 may be inserted into the central bores 32 of the upper and lower floating tools 26. A tapered mouth portion 33 of shafts 21 of the floating tools assists in guiding the bumper rods 25 into their seating position. The alignment of the parts will then be as shown in Fig. 5 with the bumper tubes being pushed to-- ward the crystal as far as they will go. If one of the bumper tubes has already been fixed into position in bushing 22, as is the usual practice only one bumper tube is pushed at this time and in this manner toward the crystal and soldered or otherwise fixed in place. Crystal support wires II are then soldered or otherwise secured to cage rods 9 as shown at [0 being careful that no stresses are introduced into the supporting wires H during the process by metallic contact between wires H and rods 9, other than that through the solder joint cast therearound. The locking pins 35 are removed and thereafter the shafts 27 from the bumper tubes 23 and 24. The crystal is then fully floated in its cage.

An alternative production method, for use in those cases where the variation in the length of crystals to be caged is in excess of three-fourths of an inch, is to proceed as shown in Fig. 4 by fixing the upper mica spacer IE to the cage rods 9 after the insertion of the crystal, and making the final accommodation for different crystal lengths through adjustment of the position of one or both of the bumper tubes.

While the invention has been illustrated to include the use of a bumper tube inserted in a bushing or grommet 22 in the mica end spacers as illustrated at 23 and 24, a Variation of the alternative caging method is possible in which the tube is omitted. In such cases, the bushing 6 or eyelet 22 itself functions asthe bumper tube. Fig. 3 illustrates such a variation and shows in detail the relative proportions of. the bumper rod 25 and the grommet 22 which acts as the bumper tube. I r 1 As an alternative construction, it will also be seen that the relations of the, bumper rods and tubes may be reversed; That is, the rods may be secured to the mica end'spacers, and bumper tubes, or the equivalent in the form of metallized bores, set into the ends of the crystal.

It will thus be seen that the invention provides a simple and effective method for caging crystals, and for aligning them accurately relative to a bumper system having improved characteristics, during their assembly. It allows a, single cage to be used with a wide assortment of sizes of crystals, in place of the many individual parts hitherto required to be handled during the caging operation.

What is claimed is:

1. In combination with a piezoelectric crystal unit having a plurality of supporting rods held in alignment by upper and lower insulating spacing disks and a piezoelectric crystal supported by resilient lead wires fixed to said rods, means for limiting displacements of said crystal, comprising a lower tubular bumper member fixed to said lower disk, an upper tubular bumper member fixed to said upper disk in axial alignment with said first tubular member, and guide members of transverse dimensions substantially less than the internal diameter of said tubes fixed in axial alignment to each end of said crystal and extending into said tubes.

2. In combination with a piezoelectric crystal unit having a plurality of supporting rods held in alignment by upper and lower insulating spacing disks, and a piezoelectric crystal supported by resilient lead wires fixed to said rods, means for preventing excessive displacement of said crystal, comprising a pair of hollow members fixed to said disks in axial alignment, and axially aligned members of transverse dimensions substantially less than the inside dimensions of said hollow members fixed at opposite ends of said crystal and extending into said hollow members.

3. In combination with a piezoelectric crystal unit having a plurality of supporting rods held in alignment by upper and lower insulating spacin disks, and a piezoelectric crystal supported between said disks by resilient lead wires fixed to said rods, a bumper system, comprising a lower bumper tube fixed to said lower insulating spacing disk, an upper bumper tube fixed to said upper insulating spacing disk in axial alignment with said short bumper tube, and bumper rods fixed in axial alignment to opposite ends of said crystal and extending freely into said bumper tubes.

4. In combination with a piezoelectric crystal unit having a plurality of supporting rods held in alignment by upper and lower insulating spacing disks, and a piezoelectric crystal supported by resilient lead wires fixed to said rods, bushing members fixed in said upper and lower disks in axial alignment, tubes extending through said bushing members, and rods of substantially smaller diameter than the inner diameter of said tubes fixed terminally in said crystal and extending therefrom into said tubes.

ARTHUR W. ZIEGLER.

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